The present invention relates to a piezoelectric device, more specifically a piezoelectric device for use in ink jet printers and a method for fabricating the same, an ink jet printer head and a method for fabricating the same.
Ink jet printers are printers of the type that liquid ink is formed in droplets or in a liquid column, or atomized to jet into the air to print letters, graphs, pictures, etc. on recording paper. Ink jet printers can be quieter, lighter and smaller, which has put ink jet printers into practical use.
Heads for use in ink jet printers predominantly use two types of head. One, where bubbles are generated by heaters in pressure chambers to jet ink out of nozzles by the force of the bubbles (bubble jet type), and a second that uses vibration plates, provided on bottoms of pressure chambers, to press piezoelectric bodies causing ink to jet out of nozzles (impact type).
Of these two types, the capability of the bubble jet type depends substantially upon the characteristics of the ink, and has its limitations with regard to its printing speed and print quality. This type has found it difficult to keep up with trends in higher speed and higher print quality.
Conversely, the impact type is capable of using inks with a wide range of characteristics, and is suitable for higher print speeds and has good controllability.
The head of the impact type has a structure exemplified in FIG. 10.
The ink jet printer head shown in FIG. 10 comprises a piezoelectric device 10, a pressure chamber plate 20 and a nozzle plate 30. The piezoelectric device 10 includes a lower electrode 14 having a relatively large area, a piezoelectric layer 16 of a piezoelectric material, and an upper electrode 18 laid on an insulating substrate 12 of ceramics or others in the stated order. In the pressure chamber plate 20 there is formed a pressure chamber 70, opened in one side of the pressure chamber plate 20, an ink feed passage 72, through which ink is fed into the pressure chamber 70 and an ink conduit 74 which leads the ink from the pressure chamber 70 through to the other side of the pressure chamber plate 20. In the nozzle plate 30, there is formed a nozzle 76 which ejects the ink.
The piezoelectric device 10 and the pressure chamber plate 20 are joined with the pressure chamber 70 in alignment with a region of the piezoelectric device 10 where the upper electrode 18 is formed, so that the ink can be charged into the pressure chamber 70. The nozzle plate 30 is connected to the pressure chamber plate 20, and the ink led through the ink conduit 72 in the pressure chamber plate 20 can jet from the nozzle 76 of the nozzle plate 30.
In this structure, a prescribed voltage is applied between the lower electrode 14 and the upper electrode 18, causing the piezoelectric layer 16, in the region where the upper and the lower electrodes are laid on top of each other, is displaced, and a pressure is applied to the ink in the pressure chamber 70. This pressure jets the ink through the nozzle 76.
The ink jet printer head of the impact type has the above-described structure.
In the fabrication process of the above-described conventional ink jet printer head, the piezoelectric device is constructed by forming the piezoelectric layer separately and then adhering the separately formed piezoelectric layer to the insulation substrate or to the lower electrode by means of an adhesive or others, or by screen-stenciling a piezoelectric material thereon.
Otherwise, the lower electrode, the piezoelectric layer and the upper electrode are laid on the insulation substrate, and then the layer body is press-adhered by a uniaxial press to thereby form the piezoelectric device. The uniaxial press is a method by which a sample is held between two flat plates, and the flat plates are pressed on both sides to apply pressure.
In the above-described conventional piezoelectric device fabrication method however, it is necessary to separately form the piezoelectric layer and adhere the piezoelectric layer by an adhesive or others to the insulation substrate. This increases the number of fabrication steps and limits the amount of simultaneous production. Undesirably from the viewpoint of fabrication cost this results in higher fabrication costs.
In consideration of the drive of the piezoelectric device it is preferable that the piezoelectric layer is thin, but it is difficult in the screen-stenciling method to form the piezoelectric layer below 50 .mu.m in thickness.
The usual piezoelectric device fabrication process uses the uniaxial press method. Owing to the convexity in the form of the upper electrode on the surface of the piezoelectric device before the press, higher pressures are exerted upon it than those exerted on the rest of the device. As a result, disuniform pressures are generated in a sample during the press which causes cracks and peels appear in a later sintering step.
Recently from the viewpoint of environmental protection, use of lead (Pb) has been positively suppressed. Piezoelectric materials of the piezoelectric devices contain lead, and it is unpreferable to use much of the piezoelectric materials. Piezoelectric materials also have high specific gravities, and it has been desirable to decrease amounts of the piezoelectric materials used in the piezoelectric devices to lighten the piezoelectric devices.